The invention relates to methods for the chromatographic isolation of vitamin E isomers. In particular to methods of isolating individual vitamin E isomers such as xcex1-tocopherol, xcex2-tocopherol, xcex3-tocopherol, xcex4-tocopherol, xcex1-tocotrienol, xcex1-tocotrienol, xcex3-tocotrienol, xcex4-tocotrienol and the like from vitamin E containing mixtures such as crude palm oil, palm oil products, palm oil by-products, vegetable oils, and the like.
Tocols are vitamin E compounds that include tocopherols (T) and tocotrienols (T3) that are found in vegetable oils in varying quantities (See, e.g., Table A). The tocols present in most vegetable oils are typically in the form of tocopherols (xcex1-, xcex2-, xcex3-, and xcex4-tocopherols). Palm oil, however, is unique since the tocols are present mainly in the form of tocotrienols (xcex1-T3, xcex3-T3, and xcex4-T3). Each of the tocols exhibits interesting physiological properties.
Both tocopherols and tocotrienols act as powerful nutritional antioxidants and help to reduce cellular damage due to free radicals arising from the body""s normal oxidative energy metabolism or from the action of toxic chemicals and pollutants in our environment. Free radicals have been implicated in aging, chronic degenerative diseases, and cancer.
Vitamin E is also a natural antioxidant, present at approximately 600-1000 ppm in crude palm oil; the major component being xcex3-tocotrienol. Recently it has been reported that xcex3-tocotrienol has anti-cancer properties in addition to its known antioxidant activity. Tocotrienols have been found to lower blood cholesterol.
U.S. Pat. No. 5,190,618 discloses a process for extracting vitamin E from palm fatty acid distillates (PFAD). The process involves converting the PFAD into methyl esters and distilling the methyl esters followed by ion-exchange chromatography and molecular distillation to get a vitamin E concentrate of more than 90%.
U.S. Pat. No. 5,157,132 discloses a process for extracting vitamin E from crude palm oil (CPO) by converting the CPO to methyl esters and then removing the esters by molecular distillation to yield carotene-rich and vitamin E-rich fractions.
GB 2,218,989 discloses converting crude palm oil into methyl esters followed by chromatographic separation of the methyl esters, on an adsorbent in the presence of solvents, to yield carotene-rich, vitamin E-rich, and sterol-rich fractions.
These patents only describe the isolation of vitamin E-rich fractions from palm oil and do not disclose the isolation individual vitamin E isomers which may exhibit important physiological properties. Thus, all of the previously known methods that involve in the adsorption/desorption chromatographic separation only isolate mixtures of vitamin E isomers rather than individual isomers. Moreover, these methods all use solvents that are costly and hazardous.
There is a need for methods to separate and isolate vitamin E isomers that avoids or eliminates the sole use of solvents and consequently, renders the process xe2x80x9cnon-hazardous.xe2x80x9d
The invention relates to a method for the chromatographic separation of vitamin E isomers from a vitamin E containing mixture. The method involves the steps of combining the vitamin E mixture with an adsorbent to effect adsorption of the vitamin E isomers on the adsorbent and selectively desorbing the vitamin E isomers from the adsorbent with a solvent under supercritical conditions.
The vitamin E isomers may be one or more of xcex1-tocopherol, xcex2-tocopherol, xcex3-tocopherol, xcex4-tocopherol, xcex1-tocotrienol, xcex2-tocotrienol, xcex3-tocotrienol and xcex4-tocotrienol. The adsorbent may be silica gel, reverse phase C-18 silica gel, or a mixtures thereof. The solvent may be CO2, propane, propene, or ethylene. Preferably, the solvent is CO2. The solvent may optionally further include an entrainer such as an alcohol. In one embodiment the separation is performed at a temperature of about 20xc2x0 C. to 150xc2x0 C. and a pressures of about 20 kg/cm2 to 800 kg/cm2. The vitamin E containing mixture may be crude palm oil, palm oil products, palm oil by-products, vegetable oils, and a vitamin E concentrate.
When the vitamin E containing mixture is a vitamin E concentrate the vitamin E concentrate may be formed by esterifying free fatty acid components of the vitamin E containing mixture with one or more monohydric alcohols to provide esters followed by removing the esters to form the vitamin E concentrate, or by trans-esterifying glyceride components the vitamin E containing mixture with one or more monohydric alcohols to provide esters and then removing the esters to form the vitamin E concentrate. The alcohol may be a C1 to C8 alcohol, such as methanol.
The free fatty acid components of the vitamin E containing mixture may be esterified using a catalyst selected from the group consisting of a solid alkali metal bisulfate acid, a solid alkali metal sulfate acid, a strongly acidic ion exchange resin, and an enzyme. The glyceride components of the vitamin E containing mixture may be trans-esterifed using a basic catalyst or an enzyme.
The present invention provides a method for the chromatographic separation of vitamin E isomers from vitamin E containing mixtures.
The phrase xe2x80x9cvitamin E containing mixtures,xe2x80x9d as used herein, means any mixture or combination of compounds that includes vitamin E. Preferably, the vitamin E containing mixture is one or more of crude palm oil (CPO), palm oil products, palm oil by-products, or other vegetable oils and fats. More preferably, the vitamin E containing mixture is one or more of crude palm oil.
In particular the present invention uses a supercritical fluid (such as SCxe2x80x94CO2) in combination with one or more adsorbents to effect adsorption and desorption of the vitamin E isomers resulting in the vitamin E isomers being separated from the other compounds in the vitamin E containing mixture. Preferably, the individual vitamin E isomers are also separated from each other.
In one embodiment the present invention involves isolating vitamin E isomers from a vitamin E concentrate. The phrase xe2x80x9cvitamin E concentrate,xe2x80x9d as used herein means a vitamin E containing mixture that has been treated chemically and/or physically to increase the concentration of vitamin E. Preferably, the vitamin E concentrate may be prepared, for example,
a. from crude vegetable oil esters via catalytic alcoholic esterification/transesterification of the vegetable oils and distilling the esters to yield the vitamin E concentrate; or
b. from unsaponifiable matters of vegetable oils and fats by a saponification process;
c. by any process, such as chromatography (solvent and supercritical) and supercritical fluid extraction.
An important feature of the invention is that liquefied gas at supercritical conditions is used in the separation. Using a supercritical fluid avoids or reduces the prior requirements for hazardous solvents. To date, there has not been disclosed any method that uses a supercritical fluid for the adsorption/desorption chromatographic isolation/separation of Vitamin E isomers from plant sources such as crude palm oil, palm oil products, palm oil by-products, and other vegetable oils and fats.
The method of the invention for the chromatographic isolation of vitamin E isomers from crude palm oil, palm oil products, palm oil by-products, vegetable oils and vitamin E containing mixtures involves combining the vitamin E containing mixtures with an adsorbent to effect adsorption of vitamin E isomers on the adsorbent and selectively desorbing the vitamin E isomers from the adsorbent, wherein the adsorption/desorption of the vitamin E isomers is carried in a supercritical fluid environment.
In one embodiment the separation is applied to a vitamin E concentrate from the vitamin E containing mixture. The vitamin E concentrate may be obtained, for example, by:
(a) Esterifying the free fatty acid component of the vitamin E containing mixture with one or more monohydric alcohols to provide esters and then removing the resulting esters by vacuum distillation or molecular distillation to provide the vitamin E concentrate. The esters may be removed via vacuum distillation or molecular distillation. The esterification may be carried out with a solid alkali metal bisulfate or sulfate acid, strongly acidic-ion exchange resin, or any effective acid as a catalyst; or
(b) Trans-esterifying the glyceride components of a vitamin E containing mixture with one or more monohydric alcohols, preferably C1 to C8 alcohols, to provide monoesters and then removing the resulting monoesters by vacuum distillation or molecular distillation to provide the vitamin E concentrate. The monoesters may be removed via vacuum distillation or molecular distillation. The trans-esterification may be carried out with a basic catalyst.
Alternatively, steps a and b may be carried out with an enzyme (e.g., candida rugosa) as a catalyst.
(c) Supercritical chromatography and/or any other chromatographic method which is effective in extracting a vitamin E concentrate from vegetable oils.
The present invention may also be applied to unsaponifiable materials as obtained by the saponification of vegetable oils.
Suitable adsorbent for the adsorption of the Vitamin E isomers include, but are not limited to, silica gel, C-18 reverse phase silica gel, and the like which are effective in adsorbing vitamin E isomers from vitamin E containing mixtures. One of ordinary skill in the art will readily be able to select suitable adsorbents for use in the methods of the invention.
Suitable solvents for use in the methods of the invention include supercritical fluid such as CO2, (SCxe2x80x94CO2), propane, propene, ethylene and the like. Preferably the supercritical fluid is CO2. The supercritical fluid may also be a supercritical fluid, such as SCxe2x80x94CO2 in combination with an entrainer. Suitable entrainers for use in the method of the invention include alcohols and organic solvents.
Typical operating conditions for the methods of the invention include pressures from about 20 kg/cm2 to 800 kg/cm2, preferably from about 50 kg/cm2 to 600 kg/cm2 and temperatures from about 20xc2x0 C. to 150xc2x0 C., preferably, temperatures from about 30xc2x0 C. to 100xc2x0 C. Individual Vitamin E isomers may be isolated with substantially higher purity (e.g.,  greater than 50%) in a single run under these conditions.
The Vitamin E isomers recovered by the methods of the invention are useful in pharmaceutical compositions, food and health food formulations, dietary supplements, and cosmetics formulations. They can also be used as fine chemicals and standard reference materials.